1. Field of the Invention
The present invention relates to a magnetic guide apparatus for guiding and running a car of an elevator along guide rails in a noncontact manner.
2. Description of the Related Art
In general, a car of an elevator is supported on a pair of guide rails which are vertically disposed in an elevation path, and the car is elevated by ropes which are wounded around a hoister. At this time, shaking of the car caused by imbalance of the load weight or movement of passengers is suppressed by the guide rails.
A contact-type guide apparatus is usually used as a guide apparatus for guiding the car in the direction of elevation. Specifically, roller guides comprising suspensions and wheels made to contact the guide rails, or guide shoes which slide over the guide rails and guide the car, are used.
In the contact-type guide apparatus, however, vibration or noise is caused by deformation of the guide rails or at joints of the guide rails. In addition, noise is generated when the roller guides are rotated. This arises a problem that the comfortability of an elevator is decreased.
In order to solve this problem, a method of guiding a car in the direction of elevation in a noncontact manner has been proposed, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. H5-178563 or Jpn. Pat. Appln. KOKAI Publication No. 2001-19286.
In the method of KOKAI H5-178563, a guide apparatus comprising electromagnets is used. The guide apparatus is mounted on the car, and magnetic force is caused to act on iron-made guide rails, thereby guiding the car in a noncontact manner. Specifically, electromagnets, which are disposed at four corners of the car, surround the guide rails from three directions, and the magnetization of each electromagnet is controlled in accordance with the size of the gap between the guide rail and the guide apparatus, thereby guiding the car along the guide rails in a noncontact manner.
The above-described KOKAI 2001-19286 discloses the use of permanent magnets in order to solve problems, such as a decrease in controllability and an increase in power consumption, which occur in the guide apparatus using the electromagnets. By using permanent magnets and electromagnets in combination, the car can be supported with a low rigidity/long stroke, with power consumption being suppressed.
In usual cases, the noncontact-type guide apparatus using magnetic force is provided with gap sensors for detecting the gap between the electromagnet and the guide rail. The magnetic force is controlled in accordance with the gap that is detected by the gap sensors, and the car is supported without contacting the guide rail.
However, in general, the guide rail is disposed in such a manner that a plurality of rails each having a predetermined length are vertically connected. Accordingly, joints are present along the whole guide rail at intervals. At the parts of the joints, there are stepped portions due to the non-uniformity of the shapes of rails and the non-uniformity of the precision in disposition of rails, and the detection signal of the gap sensor is greatly disturbed instantaneously.
In addition, in the case of using a gap sensor utilizing physical properties of an object of detection, such as an eddy-current-type sensor, the detection signal at the part of the joint of the rails is disturbed more than a degree of actual variation.
As described above, if the detection signal of the gap sensor is disturbed, the control of magnetic force is also disturbed. As a result, the car is shaken, and such a problem arises that the comfortability in riding is affected.
Jpn. Pat. Appln. KOKAI Publication No. H11-71067, for instance, discloses an invention for solving the above-described problem. In KOKAI H11-71067, there is proposed a method in which a plurality of gap sensors are provided, and sensor signals which are used are properly switched on the basis of the variation of signals of the sensors.
However, in the method of switching a plurality of sensor signals, as in KOKAI H11-71067, an input sensor signal for control becomes discontinuous, and as a result, the control of magnetic force becomes unstable. In addition, in the case where there is discontinuity between the plural sensor signals, the discontinuity is detected as a signal vibration at the time of switching, and as a result, the control becomes unstable.
There are also known a method in which an upper limit is set to the variation ratio of the sensor signal, and a method in which the variation of each sensor signal is suppressed by a low-pass filter. However, when the car is actually greatly shaken by external disturbance, this movement cannot exactly be detected and the noncontact state cannot be maintained. Besides, if the phase of the sensor signal is displaced, the stability of the control system deteriorates and thus a filter with a large-delay element cannot be used.